1. Field of the Invention
The present invention relates to an optical transmitter and relates to an optical communication system containing such optical transmitter.
2. Related Background Art
A wavelength division multiplexing (WDM) system achieves high speed and high capacity communications by multiplexing a plurality of optical signals with different wavelengths on single optical fiber or the like. In the WDM system, the transmission route from a transmission station to a receiving station sometimes changes due to, for example, a breaking of the optical fiber or a switching of the receiving station, which causes to change the transmission distance. Since the elongation of the transmission distance results in a reduction of an optical signal and a deterioration of the waveform received at the receiving station, optical amplifiers to compensate the signal reduction are provided in the transmission path. Moreover, a plurality of decision circuits each having different decision levels to each other may be provided in the receiving station so as to maintain a reliable detection of the optical signal even when the reduction of the optical signal has occurred.
However, when the optical signal is extremely degraded, problems above mentioned still remain. Namely, the optical receiver at the receiving station can not recover received signals even when the optical amplifiers are placed in the transmission path and the optical receiver provides a plurality of detection circuits.